1. Field of the Invention
The present invention relates to a plating apparatus.
2. Related Background Art
Plating apparatus have been in use for forming plating films on surfaces of substrates. In the manufacture of microdevices in recent years, it has been important to regulate film thickness distributions finely on the substrate, so as to increase the evenness in plating film thickness.
Known as an example of plating apparatus which can regulate the plating film thickness distributions is a plating apparatus comprising an annular main cathode in contact with the periphery of a substrate, an annular auxiliary cathode laminated on the main cathode by way of an insulator while out of contact with the substrate, and an anode opposing the substrate while being separated therefrom as disclosed in Japanese Patent Application Laid-Open No. 2000-54198. A DC main power supply is connected between the anode and main cathode, whereas a DC auxiliary power supply is connected between the anode and auxiliary cathode.
In the above-mentioned plating apparatus, the DC main power supply and DC auxiliary power supply can feed different currents between the anode and main cathode and between the anode and auxiliary cathode, respectively, whereby radial distributions can favorably be regulated in plating films.
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. H10-92602 and the like, it has been found that plating effected with pulsed currents can further increase the evenness in plating films.
However, the above-mentioned plating apparatus necessitates a plurality of power supplies, thereby raising the cost, which may be problematic. In particular, when each of a plurality of power supplies is a power supply which can supply a pulsed current, the cost further rises. In addition, when plating is effected with pulsed currents, the main and auxiliary power supplies must synchronize their pulses, which further complicates circuit structures, thereby raising the cost.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a plating apparatus which can regulate the plating film thickness while being low in cost.
The present invention provides a plating apparatus for plating a substrate, the apparatus comprising a power supply for generating a voltage between a pair of terminals; an anode connected to one of the terminals of the power supply; a main cathode connected to the other terminal of the power supply while in contact with the substrate; an auxiliary cathode connected to the other terminal of the power supply while out of contact with the substrate; a main resistance connected in series between the other terminal of the power supply and the main cathode; and an auxiliary resistance connected in series between the other terminal of the power supply and the auxiliary cathode.
The present invention supplies respective currents between the main cathode and anode and between the auxiliary cathode and anode from one power supply, and can set the respective current values flowing between the main cathode and anode and between the auxiliary cathode and anode by setting the main and auxiliary resistances to favorable values. As a consequence, one power supply is sufficient, so that a low-cost plating apparatus is realized. Further, when the respective current values flowing between the main cathode and anode and between the auxiliary cathode and anode are adjusted, plating film thickness distributions can be regulated, whereby a higher evenness is achieved in plating film thickness.
Preferably, the above-mentioned power supply feeds a pulsed current between the pair of terminals.
The evenness in a plating film further increases when a pulsed current is employed in plating. Since the present invention necessitates only one power supply capable of generating a pulsed current, which is relatively expensive, its cost is not much higher than that required for modifying a conventional plating apparatus. Though means for synchronizing pulses between power supplies is necessary when modifying the conventional plating apparatus, one power supply capable of generating a pulsed current applies respective pulsed currents between the main cathode and anode and between the auxiliary cathode and anode in the present invention, whereby respective waveforms of pulsed currents flowing between the main cathode and anode and between the auxiliary cathode and anode are inevitably in synchronization with each other. Therefore, a plating apparatus which can further improve the evenness in plating films can be realized at a low cost.
Preferably, at least one of the main and auxiliary resistances is a variable resistance.
This can favorably change the ratio of respective currents flowing between the main cathode and anode and between the auxiliary cathode and anode.
Preferably, the main cathode has an annular form and is in contact with a peripheral part of the substrate, the auxiliary cathode has an annular form and opposes the main cathode, an insulating layer is provided between the main and auxiliary cathodes, and the main and auxiliary cathodes have respective outer diameters different from each other.
This is favorable in that a sufficient distance can be secured between the outer peripheral face of the main cathode and the outer peripheral face of the auxiliary cathode, whereby the main and auxiliary cathodes are restrained from short-circuiting even when the insulating layer is made thinner. From the viewpoint of improving the stirrability of plating liquids in particular, it is desirable that the insulating layer, main cathode, and auxiliary cathode be made thinner.
The present invention provides a plating apparatus which can regulate the plating film thickness while being low in cost.